Various strides have heretofore made in order to produce high quality sintered powder metal articles whether in the form of gears, backing plates or the like.
Various processes and apparatus have been devised in the prior art so as to increase the density of sintered powder metal article. For example, U.S. Pat. No. 3,795,129 relates to a method of forging a sintered article having a high density which method comprises pre-heating the forging tool of a forging machine and heating a preshaped powdering article and forging said heated preshaped powder article by said pre-heated tool.
U.S. Pat. No. 3,874,049 teaches a method of forming powder metal parts having a bearing surface wherein a sintered preform is cold formed and during such forming, shear forces are applied to the surface of the preform where the bearing surface is desired by causing a moveable die to penetrate and wipe along said surface of the area of the preform.
Moreover, U.S. Pat. No. 4,059,879 relates to a method of partially densifying a selected surface portion of a sintered porous powder metal element while applying restraining pressure to other selected portions of said element in order to inhibit growth and cracking of said element during the partial cold deformation thereof. This method was described in the production of annular bearing rings and specifically required the application of restraining pressure.
Moreover, U.S. Pat. No. 4,428,778 relates to a process for producing metallic chromium sheets from metallic chromium powders comprising a step of rolling metallic chromium powders, a step of sintering rolled sheets thus obtaining a temperature in the range of 900.degree. C. to 1400.degree. C., a step of rerolling the sintered sheets with a reduction range from 5 to 50% and a step of annealing the rerolled sheets.
In many of the prior art processes and apparatus including those described above the surfaces are densified by applying a rolling cylinder or the like against the sintered powder metal article so as to densify the surface. In particular, such prior art devices generally include a "line" of contact between the densifying tool and the sintered powder metal article. More particularly in one arrangement of the prior art the densifying tool is pressed up against the sintered powder metal article which is to be densified such that the axis of rotation of the densifying tool and the rotating sintered powder metal article are generally parallel and the densification occurs along "a line" of contact. Generally speaking since such prior art sintered powder metal article are densified along "line" of contact high densifying forces are required which therefore result in lower tool life.
It is an object of this invention to provide an improved method of densifying a sintered powder metal article.
It is a further aspect of this invention to provide a method of densifying a sintered powder metal article by point contact.
It is yet another aspect of this invention to provide a method of densifying a sintered powder metal article with a tool having a point for pressing and traversing said sintered powder metal article so as to densify the surface of said sintered powder metal article traversed by said point.
It is a further aspect of this invention to provide a method of densifying a sintered powder metal article comprising: blending carbon, alloys and iron; pressing said blends so as to produce a compact; sintering said compact to produce a sintered powder metal article; densifying said sintered powder metal article at ambient temperature by relative motion between said article with the tool having a point for pressing and traversing said article to define a densified surface.
It is another aspect of this invention to produce an apparatus for defining a sintered powder metal article comprising: (a) a tool having a point for contacting said sintered powder metal article; (b) means for generating relative motion between said tool and said articles for pressing said tool into said articles so as to scribe a densified surface unto said sintered powder metal article.
It is another aspect of this invention to produce a tool for densifying a sintered powder metal blank, said tool having an edge for contacting said article at a point.